Here's what some of the bad parts looked like after sanding. I sanded the floor with an edger, using 60 and 80 grit paper. It didn't seem to take much off, so I used the belt sander with 50, 80 and 100 grit. It took off a lot more, but I gouged the floor a little when I wasn't being careful. Next time I'm going to look in to different floor sanders. The room is only 12' long, so a drum sander would only do the centre section. Next time I want to try the U-sand sander.
There were quite a few dents in the floor, and you could see where someone had a bed for a long time. The floor didn't seem in great shape, considering it's a bedroom, so it should be in better shape.
I used some stainable putty on the worst parts. I probably should have added some stain to try and match the surrounding wood. It matches the sap wood pretty good, not the darker parts.
Here it is after 4 coats of Waterlox, 2 original and 2 glossy. I sanded the floor by hand after the 3 coat, with 220 sandpaper. I used steel wool last time, but found it gets caught on parts of the floor. It had quite a bit of dust, and the sanding made the last coat come out better. It could probably use another coat to even out the gloss. The colour is a lot darker than the last room I did, using the same process. This room faces south, so maybe it's just the extra exposure to sun. Next we do the wallpaper, and we can move back in. We're going to wait until after the built-ins are done to do the trim.